The present invention relates to dental treatment appliances and more particularly to ultrasound appliances, such as appliances for removing scale, surfacing (eliminating biofilms), or cutting (cavities or preparing for a prosthesis), etc., which appliances include instruments that vibrate at ultrasound frequencies.
FIG. 1 shows an ultrasound treatment appliance 100 that comprises an ultrasound generator 110 connected to a handpiece 120 by a cord 111. A vibratory instrument 130, also referred to as a “sonotrode” or an “insert” or a “tip” that is designed to vibrate at sound or ultrasound frequencies is mounted on the top portion of the handpiece 120. In well-known manner, the handpiece 120 includes a transducer (not shown) e.g. constituted by a piezoelectric material and mechanically coupled to the insert 130 in such a manner as to transmit vibratory waves thereto at an amplitude that is determined as a function of the power delivered by the ultrasound generator 110.
As shown in FIG. 2, the vibratory instrument 130 is mainly constituted by two portions, a base or proximal portion 133 that is designed to be fastened rigidly on an element 123 that is secured to the transducer (not shown) of the handpiece 120, and a working portion or tool 132 that is designed to reproduce the vibration transmitted by the handpiece 120. The vibratory instrument 130 is generally fitted to the handpiece 120 by screw-fastening, with the base 133 of the instrument including tapping 133a that is screwed onto a fastener element 123 secured to the transducer and having a complementary thread 123a. 
The working portion or tool 132 corresponds to the “useful” portion of the instrument, i.e. the portion with which the treatment is performed. The shape of the working portion of the instrument, and in particular the shape of its end 132a, is determined as a function of the treatment to be performed. By way of example, the instrument 130 presents a working portion 132 in which the shape of its end 132a is adapted to scale-removal treatment. FIGS. 3A to 3C show examples of instruments in which the working portions or tools are of shapes that are adapted to perform the following treatments respectively: removing scale and/or foreign matter (insert 140, FIG. 3A); preparatory treatments prior to putting a prosthesis in place (insert 150, FIG. 3B); and non-traumatic extraction and disengagement treatments (insert 160, FIG. 3C). Other examples of vibratory instruments are described in particular in documents U.S. Pat. No. 6,312,256 and U.S. Pat. No. 4,283,175.
On each new treatment, and even at certain stages in a single treatment, the practitioner needs to change the instrument on the handpiece, i.e. to unscrew the base of the instrument that was previously being used and to screw on another instrument that is adapted to the new treatment or to the following step of the treatment. During a single working day, the practitioner may need to repeat this operation a large number of times. However, although this operation is not in itself difficult, the practitioner must nevertheless pay sufficient attention thereto on each occasion in order to ensure that the instrument is properly assembled. For good operation, the vibratory instrument needs to be properly screwed onto the handpiece and tightened sufficiently to obtain good mechanical coupling with the transducer, with it being possible for the transducer to use a dynamometer clamp for this purpose. Consequently, there is a need to reduce the time taken and to simplify the manipulation when changing an instrument, and more particularly when changing a working portion or tool.
Document JP 2002/065700 discloses a brush removably mounted on a tool-carrier secured to an ultrasound handpiece. Nevertheless, in that document, the system for attaching the brush to the tool carrier is adapted to allow good transmission of vibration to a brush, i.e. to a tool that is not rigid and of mass that is considerable. In addition, in the system described in that document, the coupling and attachment portions are the same. Such an attachment system is unsuitable for properly transmitting ultrasound vibration to tools or working portions that are rigid, such as those described above.